Accurately locating plugged perforations in a well-treating method



May 17, 1966 D. M. BADER ETAL 3,251,993

ACCURATELY LOCATING PLUGGED PERFORATIONS IN A WELL-TREATING METHOD Flled March 26, 1965 2 Sheets-Sheet 1 O b 4 H 7 1.. fifa. v .v ..7 ML D IA G um v AEO e a v .T5 F MA M A v R f FICB- 3- INVENTORS. DAN M. BADER, BOBBY .AGNEW,

ATTORNEY FIG. 2.

F'IG- May 17, 1966 D. M. BADER ETAL 3,251,993

ACCURATELY LOCATING PLUGGED PERFORATIONS IN A WELL-TREATING METHOD Filed March 26, 1965 2 SheefsShee1`I 2 FIG.6.

INVENTORS. DAN M. BADER,

BY B B76. NEWl ATTORNEY.

United States Patent() ACCURATELY LOCATING PLUGGED PERFURA- TIONS IN A WELL-TREATING METHOD Dan M. Bader and Bobby G. Agnew, Monahans, Tex., `assgnors, by mesne assignments, to Esso Production Research Company, Houston, Tex., a corporation of Delaware Filed Mar. 26, 1963, Ser. No. 267,993

6 Claims. (Cl. Z50-43.5)

The present invention concerns treating wells and in particular, concerns a method for accurately determining the portion or portions of the perforated interval treated and the extent of such treatment.

It is conventional practice in completing oil and gas wells to set and cement the casing and then perforate the casing either by jet or bullet perforations opposite the producing formations.

It is often necessary to open new drainage channels in the producing formation to provide commercial production or to other-Wise treat the formation. Ordinarily, casing is set through the formation and perforated opposite the formation to allow oil or gas to come into the casing from the formation. In multiple completions several casings are set and cemented in the well, and the particular casing through which production is desired is perforated adjacent the formation to be produced. The formation may -beA stimulated by acid treatment or hydraulic fracturing or treated in other Ways by injecting fluids or solids into the formation through the perforations.

However, the material injected into the perforated interval through the perforations in the casing does not distribute itself equally through all of the perforations, and in order to force the treating material through perforations other than those through which the treating material is moving to create new drainage channels in the formation, the perforations through which the material is moving are temporarily plugged with ball sealers during the treating operation.

Prior to the present invention there was no known method for accurately locating those perforations which were closed by the temporary plugs or the volume of fluids forced into the formation through such perforations before plugging thereof.

It is a primary object of the present invention, therefore, to provide an improved treating method in which perforations which have been temporarily plugged are located and the amount of uids injected into the formation through these perforations is determined.

Briefly, the invention comprises locating with a detector positioned in a Well pipe one or more of the perforations in another well pipe temporarily plugged with a ball sealer treated so as to be detectable by said detector, and determining the amount of treating uid which entered the formation through such perforation. When a heated treating iluid such as hot frac oil is being injected, a thermometer may be run with the radiation detector to locate generally the perforations taking -uidg or in any case, to locate generally the perforations taking fluid, slugs of radioactive uid may be introduced into the treating iluid and their presence determined by the radiation detector.

The above object and other objects and advantages of this invention will become apparent from a more detailed description thereof when taken with the drawin-gs wherein:

FIG. 1 is a diagrammatic, sectional View of a perforated oil well illustrating one application of the invention;

FIG. 2 is a View similar to that shown in FIG. l illustrating a further step in the same application;

ice.

FIG. 3 is a view similar to that shown in FIGS. 1 and 2 illustrating a still further step in this same application;

FIG. 4 is a view similar to that of FIGS. 1 to 3, except a different arrangement of well pipes is shown;

FIG. 5 is a v-iew similar to that shown in FIGS. 1 to 3 illustrating a different application of the invention;

FIG. 6 also is a view similar to that shown in FIGS. 1 to 3 illustrating a still different application of the invention; and

FIG. 7 is a cross-sectional view of a representative ball sealer to be used in the method of the invention.

In the preferred embodiment of the invention shown in FIGS. 1 to 3, two tubing strings 10' and 11 are arranged in a well 12 in side-by-side relationship andare cemented in place as shown. Tubing string or casing- 11 and the cement are perforated adjacent a productive formation 13 as at 14a, b, c, d, e, and f in any desired manner. In FIGS. 1 and 2, a radiation detector 15 is shown suspended in tubing string 10 on a conductor cable 16. A thermometer 17 also is suspended on cable `16 adjacent detector 15. As seen in FIG. 1, the surface apparatus includes a radiation indicator 18 and a temperature indicator 19 connected to cable 16. Tubing string 1'1 fluidly communicates with a pump 20 and a source of treating fluid, not shown, through a vconduit 21 to which is connected a radioactive ball sealer injector 22.

Once perforations 14a to f have been made, formation 13 may be treated to open it up to permit a ready passage for the oil to flow into the well. 'I'his may be done by acidizing, hydraulic fracturing, or other techniques in which a treating fluid 23 is pumped down tubing string 11 through pump 20l and conduit 21 into the producing formation through perforations 14. The treating iiuid flows through certain of the perforations; e.g., 14e-f, more readily than it flows through the others; e.g., 14a to d, and consequently, only that part of formation 13 adjacent perforations 14e-f is subjected to treatment. When the desired, predetermined amount of fluid to be introduced into formation 13 adjacent perforations 14e-f has been injected into tubing 11, radioactive'balls 24 are introduced into the treating fluid by ball injector 22 in order to force the treating fluid to act on portions of formation 13 adjacent perforations 14a-b and 14c-d, and to prevent further introduction of treating fluid into the formation through perforations 14e-f. Balls 24 are carried by the treating uid down to perforations 14e-f where the treating fluid is tlowing into formation 13. As seen in FIG. 2, balls 24 lodge in perforations 14e and 14f. The balls are held in these perforations by the iiuid pressure in tubing string 11 which is greater than the pressure in the formation, thereby effectively closing these perforations until such a time as the pressure differential is reversed and the pressure in the formation becomes greater or equal to that in tubing string 11, at which time balls 24 are forced free of the perforations and dropped to the bottom of the well as seen in FIG. 3. Radiation detector 15 is lowered in tubing string 10 and y positioned adjacent formation 13. When the radioactive ball Sealers are pumped down to stage the stimulation treatment, radiation detector 15 is raised and lowered to traverse the length of formation 1-3 to locate the perforations, in this instance, 14e-f, that took fluid by detecting radiation emanating from ball Sealers 24. The volume of iluidtaken in this stage is also readily determined by noting the amount of fluid pumped (less that in tubing string 11) when the balls seal or plug perforations 14e-f.

Radiation detector indications are transmitted to surface.

indicator 18 by conductor cable 16. A temperature survey may be used to indicate generally the perforations i taking heated fluid. For this purpose, thermometer 17 is connected to cable 16 to respond to and transmit temperature indications to surfacel indicator 19; or radioactive slugs may be injected into the treating fluid and detected by detector for this same purpose.v Another Way to determine when to inject the balls is by pressure drops of the treating fluid. Thus, during the pumping of the treating fluid through perforations 14e-f, the pressure will constantly rise until the fluid is injected into the formation, at which time it will probably drop indican ing that the formation has broken. At this time, plugs 24 will be introduced into the fluid stream to plug perforations 14e-f. When this occurs, the pressure Will again rise indicating that the fluid pressure is being exv erted against another part of the formation; c g., the portions adjacent perforations 14n, b or 14C, d. When one of these parts of the formation breaks, the pressure may again drop at which time balls Will be dropped to seal these perforations. When all portions of the formation I adjacent perforations have been treated, the formation may be produced.

In the operation illustrated in FIGS. l to 3, the portion of the formation adjacent perforations 14e-f may be a zone requiring, for example, 4,000 gallons of frac fluid; and the zones adjacent perforations 14a-b and 14e-d may be ones requiring 2,000 gallons of frac fluid. As illustrated in'FIG. 2 by the balls in dotted outline adjacent perforations 14a, b, the zone adjacent these per-forations is thevnext easiest penetrated by the treating fluid.V

In FIG. 4, an operation similar to that described with relation to FIGS. l to 3 may be carried out, except in this ligure, the arrangement of the well pipes is different. tubing string 25 is arranged within a casing 26 perforated along its length in a Yformation 27 as at 28a to f and 29a to f. As shown, radioactive ball sealers 24 lodge in and preferentially Vplug perforations 28e-'f and 29e-f adjacent the most permeable part Vof formation 27 first, While a radiation detector 15 is suspended in tubing string 25 adjacent formation 27 to locate precisely which perforations are being plugged; and the volume of fluid forced lthrough those particular perforations ahead of Sealers 24 is determinable.

FIG. 5 illustrates an operation similar to that illustrated in FIGS. l to 3 except a series of perforations in only one zone is shown. Thus, perforations 3ft in a *tub* ing string 3-1 are being selectively closed by. ball Sealers 24 to selectively close off portions of formation 32, while detector 15, arranged adjacent formation 32 in tubing string 33, detects Which perforations are being closed and when they are being closed to determine the volume of fluid forced through each perforation FIG. 6 illustrates a cementing treatment of a channel between two productive zones 41 and 42 penetrated by the Well. A tubing string 43 in the well is perforated at 44 in formation 41 and 45 in formation 42. A detector of radiation 15 is arranged in another pipe string 46 adjacent pipe string 43. ln this operation cement is pumped into pipe string 43 along with a ball sealer 24 which closes first the most permeable of the formations as, for example, formation 41 adjacent perforation 44. Detector 15 then locates this ball to'indicate which of the perforations has been plugged, and cement is then forced through perforation to seal channel 40. After the channel has been closed, a second ball sealer 24 is pumped into tubing string 43 to close perforation 4S; and detector 15V shown in dotted lines indicates closing of this perforation.

A representative ball sealer is shown in FIG. 7; and it may consist of a spherical, nylon-coated rubber element 49 provided with a slug of radioactive material 5? retained by means of a rubber plug 51. The ball may be of any material or of any shape' so long as it is capable of plugging the perforation.

Various natural Vradioactive .substances may be employed as the radioactive-material as, for example, radon,

radium bromide, radium chloride, uranium bromide, uranium petrobromide, etc. Known artificially radioactive substances also may be4 used. Y

Detector 1S may be any device responsive to radiation produced by the radioactive material as, for example, a Geiger-Mller counter, an ionization chamber, or a proportional counter.

The surface indicatingsubsurface thermometer is an available, commercial instrument.

Having fully described the operation, objects, advantages, and nature of the invention, we clarn:

1. A method for temporarily plugging perforations in a well pipe set in a borehole and accurately locating theV plugged perforations in which a formation-treating fluid under pressure is injected into said Well pipe to cause a flow of fluid through Well pipe perforations which are adjacent portions of the formation in which the back pressure is less than the pressure of the stream comprising the steps of: Y

adding plugging elements larger than the perforations in the Well pipe to the fluid stream while maintain-` ing pressure on the stream Vto cause certain of said plugging agents to lodge against perforaticns in the well pipe through which the fluid has been passing and seal them; said plugging elements containing radioactive material and being capable of detection by a radiation detector; and traversing said perforations with a radiation detector to detect the location of said plugging elements when they lodge against said perforations to locate accurately said perforations through which fluid has been passing to establish which perforations have been passing fluid, the amount of fluid such perforations have passed being Vdetermined from the volume of fluid pumped prior to sealing of said perforations with said plugging elements. 2. A method as recited in claim 1 including detecting temperature indications of said treating fluid adjacent said erforations in order to ascertain the general location of the perforations passing iiuid,

3. A method as recited in claim 1 including injecting slugs of radioactive material into said treating fluid and detecting said slugs of radioactive material with a radi ation detector in order to ascertain the general location of the perforations passing fluid. Y

4. A method for treating a formation through which a Well pipe has been set and perforated and in which the formation has characteristics such that a fluid will pass through only certain of the perforations into the formation to -treat the formation opposite said perforations comprising the steps of Cil in the well pipe which have not-been sealed by raising the pressure of the stream until the treating fluid has been forced through all of the perforations; and

passing a radiation detector adjacent said perforations to determine which of said perforations are plugged by said plugging elements by detecting the location of said plugging elements and When said perforations are plugged. Y

5. A method as recited in claim 4 including detecting temperature indications of Vsaid treating fluid adjacent said.V

perforations in order to ascertain the general locationof perforations passing fluid. Y

6. A method as recited in claim 4 including injecting slugs of radioactive material into said treating fluid and 5 5 detecting said slugs of radioactive material with a radiation 2,965,753 12/ 1960 Reynolds 25 0-435 detector in order to ascertain the general location of the 2,972,050 2/ 1961 Allen Z50- 43.5 perforations passing fluid. 3,084,250 4/ 1963 Dennis Z50-43.5 References Cited by the Examiner 5 3,093,739 6/ 1963 Danforth 250-106 UNITED STATES PATENTS RALPH G. NILSON, Primary Examiner.

2,588,210 3/ 1952 Chrisman 250-106 JAMES W. LAWRENCE, FREDERICK M. STRADER,

2,810,076 10/1957 Murdock Z50-106 Examiners. 

1. A METHOD FOR TEMPORARILY PLUGGING PERFORATINS IN A WELL PIPE SET IN A BOREHOLE AND ACCURATELY LOCATING THE PLUGGED PERFORATIONS IN WHICH A FORMATION, TREATING FLUID UNDER PRESSURE IS INJECTED INTO SAID WELL PIPE TO CAUSE A FLOW OF FLUID THROUGH WELL PIPE PERFORATIONS WHICH ARE ADJACENT PORTIONS OF THE FORMATION IN WHICH THE BACK PRESSURE IS LESS THAN THE PRESSURE OF THE STREAM COMPRISING THE STEPS OF: ADDING PLUGGING ELEMENTS LARGER THAN THE PERFORATIONS IN THE WELL PIPE TO THE FLUID STRAM WHILE MAINTAINING PRESSURE ON THE STREAM TO CAUSE CERTAIN OF SAID PLUGGING AGENTS TO LODGE AGAINST PERFORATIONS IN THE WELL PIPE THROUGH WHICH THE FLUID HAS BEEN PASSING AND SEAL THEM; SAID PLUGGING ELEMENTS CONTAINING RADIOACTIVE MATERIAL AND BEING CAPABLE OF DETECTION BY A RADIATION DETECTOR; AND TRAVERSING SAID PERFORATIONS WITH A RADIATION DETECTOR TO DETECT THE LOCATION OF SAID PLUGGING ELEMENTS WHEN THEY LODGE AGAINST SAID PERFORATIONS TO LOCATE ACCURATELY SAID PERFORATIONS THROUGH WHICH FLUID HAS BEEN PASSING TO ESTABLISH WHICH PERFORATINS HAVE BEEN PASSING FLUID, THE AMOUNT OF FLUID SUCH PERFORATIONS HAVE PASSED BEING DETERMINED FROM THE VOLUME OF FLUID PUMPED PRIOR TO SEALING OF SAID PERFORATIONS WITH SAID PLUGGING ELEMENTS. 